TWI771565B - Method for manufacturing a semiconductor on insulator type structure by layer transfer - Google Patents

Abstract

The invention relates to a method for manufacturing a semiconductor on insulator type structure by transfer of a layer from a donor substrate onto a receiver substrate, comprising the following steps: a) the supply of the donor substrate and the receiver substrate, b) the formation in the donor substrate of an embrittlement zone delimiting the layer to transfer, c) the bonding of the donor substrate on the receiver substrate, the surface of the donor substrate opposite to the embrittlement zone with respect to the layer to transfer being at the bonding interface, d) the detachment of the donor substrate along the embrittlement zone enabling the transfer of the layer to transfer onto the receiver substrate, the transfer method being characterised in that it comprises, before the bonding step, a step of controlled modification of the curvature of the donor substrate and/or the receiver substrate so as to move the substrates away from each other at least in one region of their periphery, the face or the two faces intended to form the bonding interface of the donor substrate and/or the receiver substrate being deformed so as to have a curvature amplitude greater than or equal to 136 µm.

Description

Method for fabricating semiconductor-on-insulator type structures by layer transfer

The present invention relates to the fabrication of semiconductor-on-insulator-type structures by transferring a layer from one substrate, referred to as a "donor substrate," to another substrate, referred to as a "receptor substrate."

When the semiconductor material is silicon, fabrication of semiconductor-on-insulator-type structures called SeOI, especially semiconductor-on-insulator (SOI), is usually based on a method consisting of transferring a layer from a donor substrate to a recipient substrate to implement.

According to this method, a so-called "embrittlement" region is created in the donor substrate bounding the layer to be transferred, the donor substrate is bonded to the acceptor substrate, and the donor body is then separated along the embrittled region substrate in order to transfer the layer to the receptor substrate.

One conventional layer transfer method is the Smart Cut™ method, wherein the embrittled region is created by implanting hydrogen and/or helium in the donor substrate to a predetermined depth substantially corresponding to the thickness of the layer to be transferred.

An example of the Smart Cut™ method is shown in Figure 1. An oxide layer 10 is obtained by first oxidizing (step 2 ) the donor substrate A and/or the acceptor substrate B (step 1 ), which are initially provided, typically formed of silicon, over a thickness. A brittle region bounding the to-be-transferred layer 11 is then formed in the donor substrate A by atomic implantation (step 3).

The substrates A and B are then subjected to a surface treatment so that a hydrophilic molecular bond can be formed, and then bonded to each other through the treated surfaces thus forming the bonding interface (step 4). The oxide layer(s) 10 present at the interface is referred to as a "buried oxide layer" (BOX).

The donor substrate is separated along the embrittled region (step 5) in order to transfer the layer 11 onto the receptor substrate B. This step, also known as the breaking or splitting step, can be carried out, for example, when thermally annealing the multilayer structure obtained.

The onset of separation occurs thermally through the growth of microcracks in the extent of the embrittlement region. The microcracks dispersed in the depth of the structure gradually coalesce to form a rupture line that spreads throughout the plane of the embrittled region, resulting in separation of the SOI structure from the remainder of the substrate B.

At the end of this transfer, the free surface of the transfer layer 11 opposite the surface of the donor substrate A bound to the acceptor substrate B has a considerable microroughness. This thickness represents the gradual propagation of the fracture between the microcracks. Figure 2 is a cross-sectional photograph obtained by transmission electron microscopy (TEM) of a silicon layer 12 of the donor substrate after implantation of hydrogen atoms and subsequent thermal annealing. The figure shows a fracture line 13 representing fracture propagation between the microcracks. The SOI structure is separated from the remainder of the substrate B according to the rupture line and the result is a surface with a considerable microroughness.

The roughness greatly affects the performance of electronic devices formed in or on the transfer layer. For example, substantial thicknesses cause large variations in the threshold voltages of transistors fabricated in or on this layer.

Furthermore, the roughness interferes with defect detection by laser diffraction on the final SOI structure. In fact, the roughness and the presence of some surface pores interfere with the measurement or even make the SOI structure's defects uncontrollable at lower detection thresholds.

To repair the surface and reduce its roughness, the SOI structure is typically finished by thermal, mechanical and/or chemical smoothing. The purpose of these treatments is more specifically to obtain a desired SOI thickness, as well as a smooth surface and a cured bond interface.

Although these treatments partially reduce the surface defects, an optimal surface state required for the application of the final SOI structure is usually not obtained.

An object of the present invention is to propose a layer transfer method for the manufacture of a semiconductor-type structure, which can significantly reduce the roughness of the free surface of the transfer layer.

The object of the present invention is more particularly to design the layer transfer method such that the method can reduce the roughness of the free surface of the transfer layer by controlling the formation and evolution of the rupture line at the corresponding separation or cleavage step.

To this end, the present invention proposes a method for fabricating a semiconductor-on-insulator type structure by transferring a layer from a donor substrate to a receiver substrate, comprising the following steps: a) supplying the donor substrate and the acceptor substrate, b) forming in the donor substrate a region of embrittlement bounding the layer to be transferred, c) bonding the donor substrate to the acceptor substrate and tying the surface of the donor substrate opposite the embrittled region with respect to the layer to be transferred at the bonding interface, d) separating the donor substrate along the embrittlement region to transfer the layer to be transferred onto the receptor substrate, The transfer method is characterized in that, prior to the bonding step, it comprises the step of controlled modification of the curvature of the donor substrate and/or the receiver substrate so that the substrates mutually Moving away, the face or faces that are to form the bonding interface of the donor substrate and/or the acceptor substrate are deformed to have an amplitude of curvature greater than or equal to 136 mm.

In fact, the substrate(s) are modified in an integral manner prior to bonding by applying a predetermined mechanical stress on the substrate(s), as compared to performing bonding without first deforming the substrates The curvature of the material can store additional mechanical energy corresponding to this stress in the resulting multilayer structure upon bonding.

This additional energy is released when the donor substrate appreciably begins to separate by any known means, such as by applying a mechanical stress or by a thermal treatment, and promotes the development of the microcracks and thus the formation of the rupture line. The result of facilitating the initiation and unfolding of the separation step is a reduction in the roughness of the free surface of the transfer layer at the end of the method.

According to other aspects, the proposed method, alone or in all technically possible combinations thereof, has the following different characteristics: According to a first embodiment, the curvature of the donor substrate and/or the receptor substrate is modified in an integral manner; The step of controlled modification includes depositing an additional layer on at least one of the faces of the associated substrate, the additional layer being formed of a material having a coefficient of thermal expansion different from that of the material of the substrate, the additional layer the material is selected to exert a controlled mechanical stress on the substrate that can deform it; The deposition of the additional layers is carried out on both sides of the substrate, the additional layers of the first and second sides are formed of materials having mutually different coefficients of thermal expansion, the materials of the additional layers are selected to be applying a controlled mechanical stress on the substrate that can deform it; The deposition of the additional layer is carried out on both sides of the substrate, the additional layers deposited on the first and second sides have different thicknesses, the difference in thickness being selected such that application on the substrate can deform it One is controlled mechanical stress; removing at least a portion of at least one of the additional layers after depositing the additional layers; The method includes depositing a polysilicon charge trapping layer on the acceptor substrate prior to bonding; The step of controlled deforming comprises oxidizing at least a surface area of the donor substrate and/or the receptor substrate to apply a controlled mechanical stress on the substrate that can deform it; the acceptor substrate includes a polysilicon charge trapping layer, and oxidizing the substrate includes oxidizing the charge trapping layer; depositing the additional layer is carried out by chemical vapor deposition in a reactor; Both the donor substrate and the acceptor substrate are deformed in a convex manner; According to a second embodiment, the curvature of the donor substrate and/or the receptor substrate is modified in a localized manner; The step of controlled modification of the donor and/or receptor substrate comprises the steps of: The receptor substrate is positioned on the surface of a support member having a plurality of grooves, and the surface of the receptor substrate to form the bonding interface is opposite to the surface of the support member, applying a first pressure in the grooves that is less than a second pressure applied to the face of the receptor substrate on which the bonding interface is to be formed, and while maintaining the first and second pressures, bonding the donor substrate to the receptor substrate and separating the donor substrate along the embrittled region; The face or faces of the bonding interface to be formed of the donor substrate and/or the receptor substrate are deformed to have an amplitude of curvature greater than or equal to 180 mm, and preferably greater than or equal to 250 mm.

The present invention also relates to a method for reducing the exposed surface roughness of a semiconductor-on-insulator type structure, characterized in that it comprises forming the structure by the above-described method, the exposed surface being separated from the donor body along the embrittled region obtained after the substrate.

The proposed method can fabricate SOI-type multi-layer structures by transferring a layer of interest, wherein the transferred layer of interest has a smaller thickness relative to the prior art. The method is based on controlling the modification of the curvature of the donor and/or receptor substrate prior to binding.

One-layer transfer methods conventionally involve forming a brittle region in the donor substrate that bounds the layer to be transferred. According to the Smart Cut™ method, the embrittled region is formed by implanting hydrogen and/or helium ions into the donor substrate to a predetermined depth. The selected depth determines the thickness of the layer to be transferred.

The surfaces of the donor and acceptor substrates to be bound are then subjected to an appropriate treatment to later form a hydrophilic molecule binding to the surfaces.

After bonding, the multilayer structure is thermally annealed and the donor substrate is separated from the acceptor substrate along the embrittled region, thereby transferring the layer to be transferred onto the acceptor substrate.

According to the proposed method, before bonding the substrates, a controlled stress is applied to at least one of the two substrates in order to modify the curvature of the substrate such that the substrates are at least one of their peripheries move away from each other in the area. In other words, the distance between an area of the periphery of one substrate and the area of the periphery of the other substrate to be in contact during the bonding step is relatively large after modifying the curvature of the substrate(s) concerned.

The curvature can be convex or concave in a global manner, or modified in a local manner.

"Modified in an integral manner" is used to mean modifying the overall curvature of the substrate to obtain a concave or convex shape. When the substrate has a disk shape, it has a substantially parabolic shape after deformation.

It should be understood that the terms "convex" and "concave" are relative to the curvature of the face of the substrate on which the bonding interface is to be formed, referred to as the "front face". Thus, when the curvature of the front face is convex, the substrate is referred to as "convex", and when the curvature of the front face is concave, the substrate is referred to as "concave."

"Modified in a local manner" is used to mean that only one area of the substrate (including at least one area of the perimeter) is deformed.

Whether globally or locally, the modification of the curvature does not modify the thickness of the substrate.

Examples of substrates with an overall convex or concave curvature are shown in Figures 3A and 3B, respectively.

The substrate 20 of FIG. 3A is placed freely on a generally completely flat, flat fiducial support P and has been deformed in a concave manner. The front face 21 (to form the bonding interface) is the upper face. The rear face 22 opposite to the front face 21 is parallel to the front face, and the substrate 20 has a substantially constant thickness.

The substrate 20 shown in FIG. 3B has been deformed in a convex manner. The front 21 series above. The rear face 22 is parallel to the front face 21 .

The curvature of the substrate is typically quantified by an amplitude parameter called "warp" and denoted by Bw and/or by a twist parameter Wp called "twist" and denoted by Wp.

Bw corresponds to the distance between the center point C of the median plane Pm of the substrate (indicated by a dashed line) and a reference plane P corresponding to a reference support on which the substrate is placed. In Figure 3A, the calculation is performed by using the projection P1 of the reference support on the front face of the substrate. According to FIG. 3A, Bw is negative in the case of a concave curvature, while according to FIG. 3B, it is positive in the case of a convex curvature.

The substrate is deformed to have a curvature magnitude parameter Bw greater than or equal to 136 mm. Consequently, the exposed surface roughness of the SOI structure obtained after separation of the donor substrate and transfer of the to-be-transferred layer onto the receiver substrate is drastically reduced. The exposed surface is the exposed surface of the transfer layer.

The reduction in roughness is greater than expected by the applicant, and is even more pronounced when the substrate is deformed to have a curvature magnitude parameter Bw greater than or equal to 180 mm or even greater than or equal to 250 mm.

In Figures 3A and 3B, Wp is zero because the substrate is deformed but not twisted.

The substrates may already have a specific curvature in their initial state corresponding to the parameters Bw and Wp. In this case, at least one of the substrates is deformed according to what was previously described. It is however preferred to deform the substrate to its original curvature in order to reduce the risk of breakage. Thus, if the substrate has a specific concave curvature, it can deform in a concave manner. Alternatively, if the substrate has a specific convex curvature, it can be deformed in a convex manner.

To carry out the method, it is sufficient to modify the curvature of at least the donor substrate or the receptor substrate in an integral and controlled manner during the bonding step so that at least peripheral regions of the substrates move away from each other. The energy accumulated in one or the other of the substrates upon deformation of the substrates is thus released from the peripheral region in an optimal manner when the donor substrates are separated.

Furthermore, the donor and acceptor substrates are desirably bound by free binding, in other words, the substrates can freely change their spatial configuration after binding so as to cooperate with each other. Changes in this configuration may, for example, include changes in the amplitude parameter Bw or the twist parameter Wp.

For example, a donor substrate bent in a convex manner with an amplitude parameter Bw of 30 mm prior to bonding may have a 15 mm gap still in a convex configuration after bonding on a receiver substrate that is substantially flat in the initial state An amplitude parameter Bw.

A preferred combination in an integral deformation scenario is presented below with reference to Figures 4a, 4B, 4C and 4D, and shows the substrates in their position before they come into contact for bonding.

Referring to Figure 4A, a convex curvature is applied to each of the donor substrate and the receptor substrate. In this first configuration, the two substrates 23, 24 deform in the direction of their peripheries until their peripheries move away from each other. The distance E ₂ between the peripheries of the substrates is therefore considerably greater than the distance E ₁ at the central portion thereof. This configuration is preferred because it provides a final structure with another accrued energy compared to the other configuration, and the other accrued energy further reduces the thickness of the transfer layer.

Referring to FIG. 4B, a convex curvature is applied to the donor substrate and the receptor substrate is in an initial state that may be flat or have a specific curvature. In this second configuration, the donor substrate deforms in the direction of its periphery until its periphery moves away from the acceptor substrate. Thus, for a same magnitude parameter Bw of the donor substrates, the distance E3 between the peripheries of the substrates is greater _than the distance E1 at the central portion thereof, but smaller than the distance _E2 of the _first configuration.

Referring to FIG. 4C, a convex curvature is applied to the donor substrate and a concave curvature is applied to the acceptor substrate, and the amplitude parameter Bw of the donor substrate is greater than that of the acceptor substrate. In this third configuration, both the donor substrate and the acceptor substrate are deformed in the same manner. Because the amplitude parameter Bw of the donor substrate is greater than that of the acceptor substrate, the distance _E4 between the peripheries of the substrates is greater than the distance E1 at the central portion thereof, but less than the _first configuration The distance E ₂ and the distance E ₃ of the second configuration state.

Referring to FIG. 4C, a convex curvature is applied to the receptor substrate and the donor substrate is in an initial state that may be flat or have a specific curvature. In this fourth configuration, the acceptor substrate deforms in the direction of its periphery until its periphery moves away from the donor substrate. Therefore, for a same amplitude parameter Bw of the acceptor substrates, the distance _E5 between the peripheries of the substrates is greater than the distance E1 at the central portion thereof, but smaller than the distance _E2 of the _first configuration .

According to a first embodiment, the controlled deformation of the substrate comprises depositing another layer on at least one of the faces of the substrate at high temperature. By "high temperature" is meant a temperature significantly greater than room temperature, preferably greater than 200°C, preferably greater than 500°C and in a better manner greater than 800°C.

The other layer is formed of a material having a thermal expansion coefficient different from that of the material of the substrate. Therefore, after deposition, the other layer and the substrate shrink differently when the temperature is lowered. Upon shrinkage, the other layer applies a mechanical stress to the substrate from its deposition surface, thus modifying the curvature of the substrate in a preferential direction, concavely or convexly, depending on the surface on which the deposition has been performed. The strength of this mechanical stress depends on the properties of the other layer, in particular its thickness and its constituent materials.

A person with ordinary knowledge in the art can obtain the modification of the material and thickness of the other layer to control the curvature, ie concave or convex, with respect to the material and thickness of the substrate, and to apply the parameter Bw on the substrate. a decision value.

In practice, the substrate is first placed in a reaction chamber provided for this purpose, and the reaction chamber is then heated to a heating temperature that varies with the properties of the substrate and the other layer to be deposited . Next, the other layer is deposited on the substrate. As such, the substrate and the other layer are heated during all or part of the deposition step. The same heating temperature can be maintained during deposition, or the heating temperature can be changed during deposition.

Therefore, adjusting the heating temperature of the reaction chamber can adjust the temperature difference applied to the substrate when the substrate is cooled, which in the past was lowered to room temperature, ie, about 20°C.

Deposition of the further layer is preferably carried out by CVD (chemical vapour deposition) in the reaction chamber. CVD is particularly suitable for depositing another layer that is less thick than the substrate.

According to this first embodiment, a further layer can be deposited on two opposite sides of the substrate. In this case, each additional layer is formed of a material having a coefficient of thermal expansion that is different from that of the material of the substrate.

Furthermore, the additional layers may be formed of the same material, or may be formed of different materials.

When the additional layers are formed of the same material, they have the same coefficient of thermal expansion. Therefore, care must be taken to ensure that they have mutually different thicknesses in order to apply a stress that modifies the curvature of the substrate. This can be done by depositing a greater thickness of material on one side of the substrate than on the other side during deposition, or by removing at least one of the additional layers from the corresponding side after deposition part of another layer.

When the additional layers are formed of different materials, they typically have different coefficients of thermal expansion. It is thus possible to provide two additional layers of the same thickness, or two additional layers of different thickness in order to adjust the curvature of the substrate in a more precise way. In a manner similar to the one previously described, the difference in thickness can result in an asymmetric deposition or removal of a portion of at least one additional layer after deposition.

According to a second embodiment, the controlled deformation of the substrate is obtained by thermal oxidation of the surface of the substrate. Oxidation of the material at the surface of the substrate consumes its constituent materials and forms one or more corresponding oxides. Forming the oxide creates a mechanical stress within the substrate, which in turn modifies its curvature.

The oxidizing step is performed on one or both sides of the substrate. It preferably corresponds to forming the buried oxide layer.

One side of the substrate or another layer previously deposited on the substrate as described in the first embodiment is oxidized.

Oxidation of each side of the substrate depends primarily on its constituent materials. In fact, two layers formed of different materials can be oxidized at different rates, resulting in different oxides and different thicknesses. This results in the application of different mechanical stresses on both sides of the substrate, with the result that the substrate deforms when it cools after oxidation.

The thickness of the oxide layer on each side depends on the oxidation time. A longer time oxidation can oxidize a larger thickness layer than a shorter time oxidation.

An exemplary embodiment shown in FIG. 5 relates to SOI structures fabricated on a substrate formed of high resistance silicon, with a polysilicon (polysilicon) trap layer 31 between the oxide layer 32 and the initial between the substrates 30 . The polysilicon capture layer 31 has been deposited on an initial substrate 30 and is then oxidized, thus significantly modifying the substrate's curvature. In fact, at high temperatures, the oxidation here between 800°C and 1100°C is faster on the polysilicon layer than on the opposite sides of the substrate, thus creating a large difference in oxide thickness between the two sides of the substrate . This applies different mechanical stresses on both sides of the substrate and greatly deforms the substrate when the substrate is brought to room temperature after oxidation. For example, oxidizing a 0.25 mm polysilicon layer yields a curvature of approximately 130 mm to 140 mm for a 300 mm diameter silicon substrate, and oxidizing a 0.5 mm polysilicon layer yields approximately 240 mm to 250 mm for a 300 mm diameter silicon substrate the curvature.

According to a third embodiment, the substrate is deformed by applying mechanical stress through a support or "suction cup".

This support is shown in FIG. 6 . The support member 40 is configured to receive a substrate, and one surface of the substrate is in contact with the contact surface 41 of the support member. The support has on its contact surface a plurality of grooves 42 distributed generally in a regular manner on the surface. In the embodiment of the support member shown in Figure 6, the grooves extend along two sets of parallel grooves, and the two sets of grooves are perpendicular to each other and form a square pattern extending over the entire contact surface of the support member. The troughs have vacuum suction means, advantageously in the form of a plurality of holes 43 arranged in the troughs and in fluid communication with a vacuum pump.

The support 40 is placed in a chamber provided for this purpose, and a substrate is positioned on the support. The tanks are then evacuated by the vacuum suction device. The pressure P1 in the region between the substrate and the support decreases, thus creating a pressure difference DP between the pressure P1 and the chamber pressure P2 such that DP=P1-P2<0. The pressure differential applied across different regions of the substrate creates a mechanical stress on the contact surface of the substrate. Under the action of this stress, the majority of the substrate against the support 40 is thus locally deformed. Obviously, a different pressure differential can be applied over a single portion or over several portions of the substrate to locally deform one or more peripheral regions of the substrate.

One of ordinary skill in the art can configure the support 40 and the application of the vacuum to locally deform the substrate in the desired area(s).

The pressures P1 and P2 can be adjusted to obtain a high DP that is greater than a minimum DP. When DP>minimum DP, the substrate is pressed against and fixed on the support, which corresponds to a "clamping" effect.

All parameters of the method of deforming the substrate using the support are adjusted such that all local mechanical stresses exerted on the substrate form a global mechanical stress to modify the curvature of the substrate in a global manner. The experimental parameters were also adjusted in order to control the value of the parameter Bw of the substrate.

To do this, for example, the density of holes 43 or grooves 42 in the surface of the support can be adjusted so that these holes or grooves are more in the central portion of the support than in the peripheral portion thereof. It is also possible to adjust the width of the grooves or the holes, or their orientation relative to the substrate. The value of the DP itself must be adjusted, it is understood that the larger the DP, the greater the curvature modification of the substrate.

According to this third embodiment, when the desired curvature is obtained, the pressures P1 and P2 are maintained and the bonding of the possibly previously deformed second substrate is carried out on the first deformed substrate. Therefore, the bonding is carried out while maintaining the pressure difference DP. The second substrate at least partially conforms to the curvature imparted by the first substrate as the combined wave propagates.

According to a fourth embodiment, a mechanical stress can be applied on a substrate to create a controlled bulk curvature by performing an atomic implant, or by a mechanical polishing (grinding). One of ordinary skill in the art can define operating conditions for implantation or polishing to obtain a determined curvature. example Example 1: Comparison of defects and roughness of exposed surfaces of two SOI structures

Two SOI-like structures denoted a) and b) were fabricated according to a method for transferring a layer from a donor substrate to a receiver substrate as previously described.

The structures a) and b) differ only in the curvature of the donor and acceptor substrates: For this structure a), no controlled deformation is applied to the donor and receptor substrates prior to bonding, the substrates having a specific curvature of less than 100 mm; For this structure a), a controlled deformation is applied to the donor and acceptor substrates prior to bonding in order to impose a convex curvature of greater than 50 mm on the substrates.

As mentioned above, the binding is free.

Figure 7 shows a haze map obtained by laser diffraction on the surfaces of the SOI structures a) and b), respectively, after separation and thermal smoothing by rapid thermal annealing (RTA). The laser device used is a "SURFSCAN SP2" laser device sold by KLA TENCOR.

The haze map shows the intensity of the laser signal diffracted by the surface of the structure, the properties of the surface roughness.

The haze measured over the surface of the structure a) is very non-uniform and increases from a minimum of 5.67 ppm over a large central portion 50 and below the surface to a small arc of the periphery above the surface A maximum value of 14.80 ppm on the shape portion 51, ie an amplitude of 14.80-5.67=9.13 ppm.

The haze measured over the surface of the structure b) was significantly more uniform and increased from a minimum of 6.63 ppm over a small lower portion 52 to about 8.50 ppm over a large central region 53 and reached at A 10.80 ppm maximum on an arcuate portion 54 of the upper periphery of the surface, a magnitude of 10.80 ppm - 6.63 ppm = 4.17 ppm. Therefore, the maximum haze and the magnitude of the haze measured on the surface of the structure b) are significantly smaller than the maximum haze and the magnitude of the haze of the surface of the structure a).

Therefore, the surface of the structure a) has less roughness than the surface of the structure a) and it is distributed in a more uniform manner.

FIG. 8 shows a defect map obtained by laser diffraction on the same surface as in FIG. 7 . The surface defects are detected when the diffractive laser signal exceeds a predetermined threshold intensity. The laser device used was the same as that used to obtain the haze map of FIG. 7 .

The defect distribution obtained in FIG. 8 corresponds substantially to the haze distribution of FIG. 7 .

For the structure a), the defects are numerous and mainly located on an arcuate portion 55 of the upper periphery above the surface, which means that the distribution of the defects is very non-uniform.

For the structure b), the defects are not very numerous compared to the structure a). Furthermore, the defects are distributed over the entire surface in a relatively uniform manner.

Thus, in fact, modifying at least one of the donor and acceptor substrates in an integral and controlled manner prior to bonding can reduce defects and roughness of the exposed surfaces of the SOI structure obtained after separation, and The defects and the roughness can be distributed over the entire exposed surface in a more uniform manner. Example 2: Evolution of the exposed surface roughness of an SOI structure with the curvature (warpage)

An SOI structure is fabricated according to a method for transferring a layer from a donor substrate to a receiver substrate as previously described.

A controlled deformation is applied to the receptor substrate of the structure prior to bonding to impart a convex curvature on the substrate according to different curvature values. The binding is free. The receptor substrate can be deformed by depositing another layer, by oxidizing a surface area of the receptor substrate, or by applying mechanical stress with a support (suction cup).

Figure 9 shows a haze map obtained by laser diffraction on the surface of the SOI structure after separation and thermal smoothing by RTA. The laser device used is a "SURFSCAN SP2" laser device sold by KLA TENCOR.

The haze measured on the surface of the structure decreases as the curvature increases. In fact, the region 56 with a haze of about 5 ppm increases as the curvature increases and covers a large portion of the surface. The region 57 with a higher haze of about 10 ppm corresponds to a substrate treatment region in the process, and thus remains substantially the same area.

Therefore, as the curvature increases, the roughness of the exposed surface of the SOI structure decreases. The thickness decreases when the curvature reaches 49 mm and then 89 mm, and then decreases sharply when the curvature reaches about 136 mm and then 181 mm.

FIG. 10 is a graph corresponding to the graph of FIG. 9 showing the thickness of the exposed surface as a function of the curvature. The ordinate thickness is expressed in Rq and in Angstroms (Å).

This figure confirms the observation in Figure 9 that the thickness decreases as the curvature increases. In fact, the mean value M of the undistorted roughness is about 10.6 Å, then decreases to 10.2 Å and 9.9 Å for curvatures of 49 mm and 89 mm, respectively, and finally decreases to 10.2 Å and 9.9 Å for curvatures of 136 mm and 181 mm, respectively down to about 9.4 Å and 8.8 Å.

1,2,3,4,5‧‧‧Step 10‧‧‧Oxide layer 11‧‧‧Transfer layer 12‧‧‧Silicon layer 13‧‧‧Rupture line 20,23,24‧‧‧Substrate 21‧‧ ‧Front 22‧‧‧Back 30‧‧‧Initial substrate 31‧‧‧Polysilicon capture layer 32‧‧‧Oxide layer 40‧‧‧Support 41‧‧‧Contact surface 42‧‧‧Slot 43‧‧‧hole 50‧‧‧Large center part51‧‧‧Small arc part52‧‧‧Small lower part53‧‧‧Large center part 54,55‧‧‧Arc part 56,57‧‧‧Area A ‧‧‧Donor substrate B‧‧‧Acceptor substrate Bw‧‧‧Amplitude parameter C‧‧‧Center point E ₁ ,E ₂ ,E ₃ ,E ₄ ,E ₅ ‧‧‧Distance P‧‧‧Flat reference support Pieces; datum plane Pm‧‧‧intermediate plane P1‧‧‧projection Wp‧‧‧distortion parameters

Other advantages and characteristics of the present invention can be understood after reading the following description, provided by way of illustration and non-limiting example, with reference to the accompanying drawings, wherein: Figure 1 is a diagram of a Smart Cut™-type method for fabricating semiconductor-on-insulator-type structures by transferring a layer from a donor substrate to a receiver substrate; Figure 2 shows a cross-sectional photograph obtained by transmission electron microscopy (TEM) of a silicon layer of the donor substrate after implantation of hydrogen atoms and subsequent thermal annealing; 3A and 3B show cross-sectional views of a donor or acceptor substrate having controlled global curvatures that are concave and convex, respectively; Figures 4A, 4B, 4C and 4D show schematic diagrams of several configurations of the donor substrate and the acceptor substrate at the binding interface; 5 shows a cross-sectional view of an SOI-type structure including a polysilicon layer between an oxide layer and a transfer silicon layer, according to an embodiment; Figure 6 shows a perspective view of a support or "suction cup"; Figure 7 shows a roughness map called haze map obtained by laser diffraction on the surface of two SOI structures obtained after separation and thermal smoothing by thermal annealing; Figure 8 shows a defect map obtained by laser diffraction on the surface of the SOI structure of Figure 7bis; Figure 9 shows haze plots for different values of curvature (Bw) obtained by laser diffraction on the surface of an SOI structure obtained after separation by thermal annealing and thermal smoothing; FIG. 10 is a graph showing the evolution of the thickness of the exposed surface as a function of the curvature, corresponding to the haze graph of FIG. 9 .

20‧‧‧Substrate

21‧‧‧Front

22‧‧‧behind

Bw‧‧‧amplitude parameter

C‧‧‧Central point

P‧‧‧Flat datum support; datum plane

Pm‧‧‧intermediate plane

P1‧‧‧Projection

Claims (15)

A method for fabricating a semiconductor-on-insulator type structure by transferring a layer from a donor substrate to a recipient substrate, comprising the steps of: a) supplying the donor substrate and the recipient substrate, b) forming in the donor substrate a region of embrittlement bounding the layer to be transferred, c) bonding the donor substrate to the receptor substrate, the donor body opposite the region of embrittlement with respect to the layer to be transferred The surface of the substrate is at the bonding interface, d) separating the donor substrate along the embrittlement region, so that the layer to be transferred is transferred to the acceptor substrate, the transfer method is characterized in that before the bonding step, The method comprises the steps of: controllably modifying the curvature of the donor substrate and/or the receptor substrate to move the substrates away from each other at least in an area of their isoperipheries, to form the donor substrate The face or both faces of the bonding interface of the substrate and/or the receptor substrate are deformed to have an amplitude of curvature greater than or equal to 136 μm. The method of claim 1, wherein the curvature of the donor substrate and/or the recipient substrate is modified in an integral manner. 2. The method of claim 2, wherein the step of controlled modification comprises depositing an additional layer, the additional layer is formed of a material having a coefficient of thermal expansion that differs from that of the material of the substrate, the material of the additional layer being selected to impart a controlled deformation on the substrate mechanical stress. The method of claim 3, wherein the deposition of the additional layers is carried out on the two sides of the substrate, the additional layers of the first and second sides are made of materials having mutually different coefficients of thermal expansion Formed, the materials of the additional layers are selected to impose a controlled mechanical stress on the substrate that can deform it. The method of claim 3 or 4, wherein the deposition of the further layer is carried out on the two sides of the substrate, the further layers deposited on the first and second sides have different thicknesses, the difference between the thicknesses is selected so as to exert a controlled mechanical stress on the substrate that can deform it. 5. The method of claim 4, wherein after depositing the additional layers, at least a portion of at least one additional layer of the additional layers is removed. The method of claim 1, comprising depositing a polysilicon charge trapping layer on the acceptor substrate prior to bonding. 2. The method of claim 2, wherein the step of controlled deformation comprises oxidizing at least a surface area of the donor substrate and/or the receptor substrate to apply a controlled deformation on the substrate mechanical stress. The method of any one of claims 7 and 8, wherein the acceptor substrate comprises a polysilicon charge trapping layer, and oxidizing the substrate comprises oxidizing the charge trapping layer. A method as claimed in any one of claims 2 to 4, wherein depositing the further layer is carried out by chemical vapor deposition in a reactor. The method of any one of claims 2 to 4, wherein both the donor substrate and the acceptor substrate are deformed in a convex manner. The method of claim 1, wherein the curvature of the donor substrate and/or the recipient substrate is modified in a localized manner. 4. The method of any one of claims 1 to 4, wherein the step of controlled modification of the donor and/or receptor substrate comprises the step of positioning the receptor substrate on a support having a plurality of grooves On the surface, the surface of the receptor substrate to form the bonding interface is opposite to the surface of the support member, and a first pressure is applied in the grooves, and the first pressure is higher than that applied to the surface of the bonding interface to be formed. A second pressure on the face of the acceptor substrate is small, and while maintaining the first and second pressures, the donor substrate is bonded to the acceptor substrate along the embrittlement The regions separate the donor substrate. The method of any one of claims 1 to 4, wherein the face or faces of the bonding interface to be formed of the donor substrate and/or the acceptor substrate are deformed to have a curvature greater than or equal to 180 μm magnitude. A method for reducing the exposed surface roughness of a semiconductor-on-insulator type structure, characterized in that it comprises a method as claimed in claim 1 The method of any of to 4 forms the structure, the exposed surface obtained after separating the donor substrate along the embrittled region.

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